Electron beam system



3 Sheets-Sheet l /NVENTOR R. KMPFNER BV R. KOMPFNER ELECTRON BEAM SYSTEM Nov. 5, 1957 iled oct. 1o, 1952 ATTORNEY Nov.`5, 1957 R. KOMPFNER 2,812,467

ELECTRON BEAM SYSTEM Filed oet. 1o, 1952 s sheets-sheet 2 /Nl/E/VTOR R. KOMPFNER A TTORNE V Nov. 5, 1957 R. KOMPFNER ELECTRON BEAM SYSTEM 3 Sheets-Sheet 3 Filed Oct. l0, 1952 MNM.

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'//VVE/VTOR R.'KOMPFNER ATTORNEY 2312.461 snaar-RONBEA-rvrsgr-STEM` a y Rudolf Kompfner, Far Hills, N-.;Jj.,i.assignor Ktty-Bell Telephone Laboratories, Incorporated, `New AYork, N. Y., a corporation of New 'YorkN A n Application October 10, 1952,"Serial 0.314,192

,16 claims. ,totals-3.5)

This invention relates toelectron-'beam systemsfand more particularly to such-systems for providing'fhigh density annular electron streams for'utilization in radio frequency apparatus. x

Typical of radio frequencyapparatus-whichcanadvantageously incorporate electron beam'systems in *accordance with the invention `is'the-traveling wave tubewhicli employs the interaction between an electron streanrand aV traveling electromagnetic wave over a pluraiityofoperating wave lengths to secure ampliiication-of the'electromagnetic wave. in such a tube, the electron stream is projected longitudinally close past awave transmission circuit along which kpropagates the electromagneticwave, and it is desirable to .minimize transverse components in the electronv stream Which'are set up by vspace charge effects. It has generally been the practice, hitherto, to employ strong longitudinal magneticelds tn reduce such transverse components. Howeven such magnetic 'elds require either large permanent magnets which are vwasteful of space or else bulky solenoids whic'hare wasteful of both space and power.

One object of the present invention is tominimize the need for magnetic focussing for maintaining the vvelectron flow cylindrical in electron beam systems vsuitable for radio frequency applications.

Additionally, in such traveling wave tubes,'when high power output is desired, it is important to utilizeele'ctron streams of high current densities. kHowever, hitherto, it has been difficult to achieve as high densities asis desired, kboth because of limitations on`V the -emissioneowof a given cathode area and because'of Vtheilargespace` charge forces set up in high density streams whichtend to cause the-stream to diverge. p l

Another object of the present inventionfis `to facilitate the realization and use of high density 'eiectronistreaifns A related object is to improve the power handling," capacities of radio frequency apparatus which'ernplo'y'electron streams. Y

In an article entitled Axially'SymmetrieElectronBeam and Magnetic Field Systems, by 'Lr A. -Harris on pages 700 through 708 of-the June i952 issue oftheProceedings of the Institute of-Radio Engineers, there is described an electron beam system in which transverse-'components of an annular electron stream-are minimizedv by first imparting a rotational component-to the-electrons-inthe l stream and then projecting vthe electrons through- Tan annular passage formed between -two cylindrical electrodes between which exists'a radial electriciteld. flhevvarious parameters areadjusted softhat equilibrium fis vmaintained between the radially outward space charge/:forcesiinfthe stream, the centrifugaldorces on the electrons .resulting from the rotational. component, andthe radially inward forces resulting from `theD.-C.- electrictieldiset between the two cylindricalv electrodesfdeiiningr-the.spathxiof travel ofthe stream. To-this end, an annulartcathode is placed inside a magneticallyshielded structurewhich is apertured for passage therethroughof,.the. cylindrical Y 2,812,461 i. Patented Nov. 5,v 1957 ice i 4magnetict'eld is set Aupacross 'the aperture in the strucuture for imparting a rotational twist to the electrons in "thebeam Vas theyeitit therefrom. Thereafter, 'this elec- '.tr'onbeam directed valong an annularpassageiformed betweengtwo cylindrical 'electrodes across 'which there is maintained a radial electric rfield-for creating a radially inward force. The. parameters are suitably rrelated so :that the vvarious ,forces are balanced and electron --liow throu'ghgthe 'passage between. the two electrodes remains cylindrical.A However, it appears that an electron beam system of this "typegwhen 'designed for providing electron streams suitablefoimicrowave tubes will ordinarily require' largeradial magnetic'iields, a factor which consider- `ably diminishes its usefulness for such applications.

IAAThe'y present invention relates toimprovementsinfthe electron beam system of the above-described typewhich betteradaptit for incorporation-in radio frequency apparatus, 'as 'for example, traveling wave tubes. In particu- "lar, since ythest'rength of the-,radial magnetic'tieldnecessary togive rotational momentumto -the electrons is y.inversely.related.to rthe cross sectional area ofthe beam, ritis advantageousto make the cross-sectional area ofthe "bearh'large at the point where it traverses'the region of radial magnetic lield Y so 'that a small radial magnetic leid will su'iiice Additionally, in order to achieveelec- "tron beams of high current densities it is generally advantageous to utilize initially vthe emission from a cathode r'surface large-.in comparisontothe desired beamcross section since there arepractical'limits on the emission availv able for a given surface area and, thereafter, to concentrate the electrons into abeam of the desired cross 4sectiQnfTo these lends, in an electron .beam system in .accordance.withtheiinventiom there is utilized an .annular `cathodep'fl relatively large surface and its emission is made to 'conv'er'geto. annular cylindrical flow of relatively ,smaller cross sectional? area, zthe rotational momentum, lvhowever, beingiimparted ,to the electrons at apoint where fthe beamisistilloflarge cross section. As a result, there anf'overtaxing ofthe emission properties ofthe cathode, 'and at'th'e same timethereis minimized thestrength of the radialmagnetieeld. necessary for imparting the de- ,s'iredrotatiom'thereby efectingstill greater economies in magnetic lux. VMoreover,- by` yreducing `the radial magnetic iieldfnecessary, ,the.resultingasimpliication of design of. the` magneticallytshielded structure makes possible rthe fincorporationof other features lofthe invention. -In particular, since in order to achieve a radial magnetic iield 4over ,the entire annular beam, itwill generally be Anecessaryftoemploy an .axial yoke which passes through the cathode, lthedesign requirements-on this yoke -Will tbe y :considerably lightened, making l practical the nsevofa holi low yoke. Thisrinturn, permits radiofrequency connection tothey axisof the electron beam which is. often-desirable vin .microwavetube applications, as will be described more :fullyhereinaften r. f l

,Additionallyt,isdesirable tominimizetransverse components,intheelectronrbeam which tend tobe setaupl inthe region `,between `the point `at which'y the VelectronsV traverse electron beam emitted from the cathode, and a `,radial the region of radial magnetic iield and the point at which .the electrons :enter theregionfof radial l electric field.v To

. `,this' .lend, v.ini accordance .withzthe inventionfthe .region of Moreover, it is possible in accordance with another feature of the invention to eliminate completely the 'need for magnetic fields. To this end,electrostatic fields are employed to introduce the desired rotational components to the electrons in the beam.

Additionally, for particular application to traveling wave tubes, it is in accordance with still another feature of the invention to utilize one of the two electrodes which define the annular passage for the flow of the electron beam as a wave transmission circuit along which propagates the electromagnetic wave for interaction with the electron flow. In an illustrative embodiment to be described hereinafter, the inner electrode is a helical con ductor along which propagates the electromagnetic wave. In this embodiment, it is convenient to utilize a radio frequency connection to the axis of the electron beam of the kind mentioned above. In another illustrative embodiment tobe described, the `outer electrode is a corrugated conductor along which propagates the electromagnetic wave.

Various other objects and features will appear to a worker skilled in the tube art from the following more detailed description. Moreover, it will also become evident that the various features to be described can be employed either singly or in combination. The invention will be described in conjunction with the following drawings in which:

Fig. l shows schematically in longitudinal section a traveling wave tube which incorporates an electron beam system in accordance with 'the invention and which is characterized by coaxial input and output coupling connections to the inner of the two electrodes which define the annular passage of electron flow;

Fig. 2 shows schematically in longitudinal section the electron gun end of a traveling wave tube which incorporates an electron beam system in accordance with the invention and which employs a hollowwave guide input coupling connection to the inner of the two electrodes which define the annular passage of electron fiow;

Fig. 3 shows schematically in longitudinal section the electron gun end of a traveling wave tube which includes an electron beam system in accordance with the invention and which makes use of wave guide input coupling con-` nections to the outer of the two electrodes which form the annular passage for electron flow; i g

Fig. 4 shows schematically in longitudinal section taken along line 4 4 of Fig. 5, the electron source end of a traveling wave tube which utilizes an electron beam system in accordance with the invention employing electric fields to impart rotation to the electrons in the beam; and Fig. 5 is a transverse section taken along line'S-S of Fig. 4.

With reference now to the drawings, Fig. 1 shows by way of example, a traveling wave tube which employs an electron beam system in accordance with one aspect of the invention. In the interest ofrsimplicty most of the various supports, spacers and like structural details have been omitted. At one end of an evacuated tubular glass envelope 11, there is positioned the electron gun 12 symmetrically disposed around the longitudinal axis of the tube and, at the opposite end in target relationship therewith, there is positioned a suitable-collector electrode 13, similarly disposed symmetrically with the longitudinal axis of the envelope. V

The electron gun 12, which is shown schematically, can be substantially of the kind known as the Pierce type, the principles of which are set forth in Chapter X of a book by I. R. Pierce entitled Theory and Design of Electron Beams, published by D. Van Nostrand Co., Inc., New York (1949). Such an electron gun comprises essentially a cathode 14, a heater (not shown) and anv electrode system'A for shaping and accelerating the electron beam. In this particular embodiment, the electron emissive` surface of the cathode 14 is an annular spherical zone. The electrode system basically compri-ses an annular beam shaping electrode 15 partially enclosing the cathode 14 and an annular accelerating anode 16. This electrode system is designed to form the electrons emitted from the cathode 14 into a convergent conical annular beam. Suitable lead-in conductors are provided to the various elements of the electron gun through the glass envelope from suitable voltage supply sources. The various design considerations applicable in deriving the desired flow configuration are set forth in the above-mentioned Pierce book. This electron gun is to be supported in a magnetic field free region, and, accordingly, it is enclosed by a magnetically shielding structure 17. This structure, which is of a suitable magnetic material such as iron, comprises a central inner portion 18 including a hollow axial yoke 19, an intermediate portion 20, and an outer portion 21 external to the envelope. The three portions of the structure are aligned in the manner shown to form a substantially continuous magnetic shield around the cathode except for the annular aperture 22 which is aligned with the cathode 14 in the direction of electron flow. In operation, the electron beam exits through this aperture. A solenoid 23 external to the envelope is used to create magnetic ux through the shielding structure 17 for establishing a magnetic field across the two opposing surwhen the beam is still of considerable cross section.

faces 22A and 22B of the annular aperture 22. Alternatively, a portion of the shielding structure can comprise permanent magnets for forming a magnetic field across the two opposing surfaces of the annular aperture 22. There is maintained a D.-C. potential difference between the inner and intermediate portions of the shielding structure by suitable lead-in conductors connected to a voltage supply source; To this end, the inner and intermediate portions 18 andr20, respectively, of the structure 17 are maintained electrically insulated from one another. There results a radial electric field between opposite surfaces of the annular aperture 22 since the outer surface 22B is associated with the intermediate portion 20 while the inner surface 22A is associated with the inner portion 18. In this way there is simultaneously .applied to each electron as it traverses the annular aperture 22 a radial or transverse magnetic field which imparts a rotational velocity component thereto and a radial or transverse electric field which creates a radially inward force which acts to maintain equilibrium between the various transverse forces acting on each electron. As has been indicated above, in order to minimize the strength of the magnetic field needed to impart the necessary rotation, it isadvantageous to induce thisrotational component to the electron beam at a point It is also advantageous to adjust the geometry of the surfaces of the annular aperture 22 and the strength of the electric and magnetic fields thereacross to cooperate in effecting the convergence of the there substantially conical stream into a substantially cylindrical annular beam at a region beyond this aperture. To this end, there are also provided electrodes 25 and 26, each symmetrically disposed about the tube axis and extending therealong toward the collector end of the tube for forming between them an annular passage for the cylindrical electron beam. To provide the desired radially inward force on the electrons, the inner electrode 26 is maintained at a positive potential Y with respect to the outer electrode 25 by means of lead-in i forms a continuation of the path of electron flow between the aperture 22 and the passage 27. To minimize disturbance of the magnetic field across the aperture 22, electrodes 28 and 29 `are of non-magnetic material. Lead-1n either with portions of the shielding structure QI with.. the

tentials on vthese electrodes also serve to control the longi atlanti tentials and thegeometry of theelectrostaticflensa .e ablychosen to elect theconvergence. of.T the .conical beam of relatively largefcross section exiting .through aperture 22 into.. acylindrical beam of relativelyrsmaller cross section for travel throughlpassagel27. v Theenvelope of the electron stream is shown by the broken lines. 3,0. It is possible to associate elementsA of this electrostatic ,lens

two electrodes forming the passage '27. In the embodiment here shown, the outer electrode 29 of the welectrostaticl'ensis a flared extension of the-.outer electrodev'ZS While the inner electrode'28 of the l'ensifsanon-magne'tic tapered projection brazed to andextending axiallyfrom the yoke 19 of the magnetic shield 17 into 'the region enclosed by the outer electrode, 29.

l Theipotential difference provided betweenthe. outer and vinner electrodesZS and 26is adjusted tofcreate a vradially `inward- 'force which balances the radially outward space charge forces and the centrifugal force resulting from` the electron rotation. In the previously identified Harris paper, there are set forth the various design relationships to `be satisfied for eifectingthe desired balance. `The potudi-nal electron stream velocity.

`At the collector end of the electron path, the outer electrode is outwardly flared to provide afield configura-tion -which causes divergence of the electron-flow away from rthe tube axis. This change in ow direction diverts most of the electron beam into the collector electrode 13 which preferably is maintained at a positive potential with respect to the electrodes 25 and 26. This collector electrode is preferably a'hollow yannular enclosure open at one end for admittance of the electron beam and oriented to surround the divergent electron flow in a mannerto minimize secondary electron emission whichis 'generally undesirable.

This tube shown in Fig. 1 is particularly adapted for coaxial input and output` connections to the wave transmission circuit. Input waves are applied vto the coaxial input terminal 31 at the electron gun end of the tube which comprises an inner conductor 32Jwhich is an extension of the inner electrode 26 and an outer conductor 33 which is an extension of the axial yoke 19 ofthe shielding structure 17. The inner conductor 32'passesthrough the hollow yoke v19 of the shielding structure 17 for con-nection to the inner electrode 26. The diameter of this, inner conductor gradually increases as it progresses inwardly into the tube until it matches thediameter of .the inner electrode 26 to which it is connected. The inner electrode 26 preferably is a tubular cylindrical conductor tapering gradually at each end and which has va helical grooving 35 so as to be effectively a helical ribbon conductor of the lkind which is suitable as a wave transmission circuit. For broad band matching purposes, the pitch of this grooving 35 .decreases with distance away from its. two ends being substantially constant along the major-central portion. As is Well known, the pitch of this growing determines the axial velocity of waves propagating therealong, the term pitch meaning the distance measured axially Ibetween corresponding points on adjacent turns OLy grooves. e

From the coaxial output terminal 37 at the .collectorr .Sud of the tube, .output waves are abstracted forrutilization.

. The coaxial output terminal 37 resembles the input terminal 31, The inner conductor 38 is essentially an axial extension of the inner electrode .26', being a tapered conductor which is connected to VtheendofY the tubular Vconductor which serves .as the inner electrode 26. 1Theouter conductor 39 is a tubular cylinder which extendsinto the tube for surrounding the inner `conductor 3,13 Slightly bevond the regionvto which-the latter viscc/nnected to the yinnen" electrode 26. It isl ofcourse necessary that both .the input and output terminals bevacuumtight.

a 'high densitycylindrical beam, ,proj ecte'd past the inner lectrode.zferlihteractiag with the electromagnetic wave propagatin-g'therealong, and finally gathered in the collector electrode. 13. v

For yconventional traveling wave tube operation, the

pitch of the ygrooving,.35 in the inner .electrodev 26 is :chosen to provide an axial wave velocity substantially 4equal to the longitudinal electron beaml velocity. However, this tube canconvenientlyr bev utilized forspatial harmonic type. operationzof the kind .described in copending application Serial No. '99,757, tiled lune A17, l1949,

'now S.. Patent 2,683,238, issued .luly 6', 1954, to S.

Mil'lman.. In such operation, vthe relative velocities of ,therelectron stream andthe vtraveling wave are adjusted so that a particular group of electrons will see the same Vphase of the electric field at successive traversals of the gaps, of Vhigh electric field kcorresponding to the groovings in ,the tubular inner electrodev 26. Alternatively, this tube aswell as the other embodiments to bev described, fcl'anvconveniently be operated as backward wave tubes in .,whichthe. useful'v interaction occurs between the electron lbeam and an oppositely directed traveling wave. Operation of. this kind 'is described in copending application .seria No.. 288.437. IedMayU. k1952. by a. Kampeer,

and copending applicationl Serial No.,288,438, led May 17, "195,2, by R. Kompfner and N.. T. Williams.

fig. 2 shows the. electron gun end of a traveling wave tube l11,0 which utilizes an electrongbeam system slightly modified from that utilized in the tube.10 shown in Fig. l. Additionally, tube 110 is designed particularly for use withjhollow wave guide input and output connections to the virner ofthe two electrodes dening the major portion ot the path of electron flow. .(However, in the 'interest of simplicity,` elements in thistube corresponding .to elejrnents 'of tube 10 have generally been designated by reference characters which diier by one hundred from those klof the corresponding elements of tube 10. i In tube i110,

,theelectrons emitted from the cathode v1 14 are formed into an annular cylindrical beam of relatively large cross ysectional area. Then after the electrons in this beam have been given their rotational impetus, this beam is convergedvi'nto anfannular electron beam of relatively smaller cross sectional area. To this end, cathode 114 which serves as the vsource of the electron stream is an annulus .of relatively large inner and outer diameters.

The electrons emitted are formed by means of the beam shaping Velectrode and the accelerating anode 116 into an annular cylindrical beam of relatively large inner and outer diameters. This large beam then passes through the aperture 122 in the shielding structure 117 which encloses the electron gun, and at this time there is impartedto ita rotational componentby the radial magnetic fieldl created by solenoid 123 which exists across the aperture122. Moreover, as in the tube described in Fig. l, there is also provided a D. C. electric eld across the opposite .surfaces '7122A and 122B of the aperture 122 which provides a radiallyinward force to balance the radially outward space .charge and centrifugal forces. There are also provided outer and inner electrodes 1.25 and 126 which extend along the major amplifying portion o f the tube length and `which between them define an annular passage 127 for the .electron flow. The inner electrode .126 ,is aghelical .ribbon conductor which serves assth'e wave transmission circuit. Between the annular passage .127 and thevaperture 122, there is-positioned an .electrostatic lens cnmprising electrodes 128 and,129 for I reforming the cylindrical beam. exiting from` aperture -122 i 7` through passage 127. Lead-in `conductors (not all vof which are shown) Vfrom voltage supply sources provide suitable `operating potentials on the various elements.

The electrode 128 can be a non-magnetic projection from the inner portion of the shielding structure and also be integral with the inner electrode 126.` The surfaces of electrodes 128 and 129 and the potentials applied thereto areadjusted to provide the desired convergence of the electron flow.

In tube 110 input waves are supplied to the inner electrode 126 by way of a hollow wave guide input connection of the kind well `known for coupling to the helical wave transmission circuit of a helix type traveling wave tube. The input connection comprises a section of standard rectangular hollow wave guide 140 which has a pair of opposite side walls apertured for the passage therethrough of the tube envelope 111. This wave guide section is closed off at one `end while the other end can be a continuation of a wave guide transmission system. The inner electrode 126 is in field coupling relation with the wave guide 140 along a coupling region 141.` The grooving 135 of the inner electrode 126 preferably begins at the electron gun end of the coupling region 141 and decreases in pitch therealong. The length and positioning of this coupling region is adjusted to provide optimum coupling between the wave guide 140 and the inner electrode 126 and also to be suciently small as not to create any significant disturbance in the radial electric field configuration in this region. For conventional amplifier applications, output energy can be abstracted from the inner electrode 126 at the collector end in a correspondingfashion. Alternatively, for backward wave ap plications output energy will, be abstracted by way of wave guide connection 140 in the way now well known for suchapplications.

The tubes shown in Figs. land 2 have each made use of the wave circuit of the inner of the pair of electrodes forming the annular passage for the cylindrical electron beam in accordance with one aspect of the invention. For some applications, however, it may be desirable to employ an electron beam system of the kind described above in a way to utilize the outer of the pair of the electrodes forming the annular passage for the cylindrical electron beam. Fig. 3 illustrates an embodiment of this kind.

Fig. 3 shows the electron source end of a traveling wave tube 210 which embodies an electron beam system in accordance with the invention in a manner to utilize as the wave circuit the outer of the two electrodes defining the annular longitudinal path of electron flow. ln many respects, the electron beam system of this tube resembles that of the tube shown in Fig. 2. Accordingly, for purposes of simplicity, elements shown in this figure corresponding to elements shown in Fig. 2 are designated by reference numerals which are one hundred larger than corresponding elements of the tube shown in Fig. 2. The annular cathode 214 provides an electron beam which is formed into a cylindrical annular beam for projection past the aperture 222 in the shielding structure `217. Across the aperture 222 there is set up a magnetic field which imparts a rotational component to the beam. An electrostatic lens formed by electrodes 22S and 229 serves to converge the annular beam emitted into an -annular beam of relatively smaller inner and outer diameters whereby the density of the stream is increased. This compressed annular beam is thereafter projected along an annular passage formed between electrodes 225 and 226. The inner electrode 226 is a cylindrical rod which extends along the longitudinal axis of the tube, and can be for convenience attached at one end to the shielding structure 217. The outer electrode 225 which, in this case, also serves as the elongated portion of the envelope of the tube extends disposed around the inner electrode 226. The outer electrode 22S comprises essentially a hollow circular wave guide whose inner walls are corrugated to provide transverse slots 245 for reducing the phase velocity of waves propagating therealong. As has been indicated above, this outer electrode serves as the slow wave circuit along which travels the electromagnetic waves for interaction with the electron beam. A conventional hollow wave guide coupling connection is provided at the electron source end of this wave circuit. This coupling connection comprises a section of hollow wave guide 240 which is provided with a glass window 242 through which input energy can be supplied, or output energy abstracted, as the particular tube application demands. One end of outer electrode 225 extends into the wave guide 240 for coupling thereto and the depth of the transverse slots 245 increases with progress downstream for improving the band width characteristics of the coupling. A longitudinal slot 243 serves as a radio frequency choke for concentrating the flow of energy from the guide 240 for travel downstream along the wave circuit. Coupling connection can be provided at the collector end of the wave circuit in an analogous fashion. The operation is essentially as described for the tube shown in Figs. 1 and 2.

Each of the electron beam systems of the various tubes described above has utilized a magnetic field for imparting a rotational component to the electrons as they exit from the shielding structure. Alternatively, however, each of these beam systems can be modied to employ an electrostatic eld to impart the desired rotational component to the electrons. ln the tube 310 of which the electron gun end is shown in Figs. 4 aud 5, there is incorporated such an electron beam system. ln other respects, the tube 310 is essentially similar to tube 110 shown in Fig. 2. Accordingly, elements of tube 310 corresponding to elements of tube 110 are designated by reference numerals two hundred larger than such elements of tube 110. To achieve the electrostatic field configurations desired, conductive vanes 350 are attached to the portions 320 and 318 of the structure 317 for extension across the aperture 322 as illustrated in Fig. 5. Because of the absence of the magnetic flux, it is less important to employ the structure 317 for magnetic shielding and instead this structure is useful primarily in establishing the desired electric elds. Successive varies extend alternately from portions 320 and 318 of the structure 317 to form an interlaced or interdigital circular pattern, Lead-in conductors from a suitable voltage supply connected separately to portions 320 and 318 establish a potential difference therebetween which causes a corresponding potential difference between successive vanes. Accordingly, there exists in each of the regions 351 between adjacent varies and through which the electron beam is projected a tangential electric field whose direction reverses between adjacent regions but which is always normal to that of electron motion. As the electrons penetrate such regions, there is imparted to them a rotational component, the direction of such rotation reversing for electrons passing through adjacent regions. Effectively, there is set up in the region beyond the aperture 322 two counter-rotating electron beams. However in operation this difference in rotation will usually have little effect and for present purposes the two beams can be treated as one. Thereafter, this beam of rotating electrons is converged in any of the ways set forth above into a relatively higher density beam for projection along the annular passage 327 formed between the two cylindrical electrodes 325 and 326. It can readily be seen that this electrostatic arrangement for achieving the desired electron rotation can readily be employed in the electron beam systems of the tubes shown in Figs. l, 2 and 3.

It should also be evident at this point that the various improvements incorporated in the electron beam systems described can be utilized either singly or in combination. Similarly, it should also now be evident that electron beam systems incorporating such improvements can find iapplicationinea; variety of,` electroniccdevices. Accord- 1ing1y,.it1 is t'obe understood that the various embodiments described arev merely illustrative: of theprinciples of the invention. v Various other arrangements can be devised by ai worker ini the art `without departing from the spirit and '.scop'e of the invention.

What is. claimedl is: ,1.-In combination, anr electron source' 2 for forming, lan annular ,electron beam of-relative'ly large `cross section,

ai structure partially enclosing s'aid source and having an ulfarape'rtre for the passagev therethrough of the annular beamof electrons andsevere'd for maintaining .DL-Ct isolation between the two opposite lsurfaces ofthe annular aperture,nieans tor-imparting a rotational comportent' tothe electrons inl saidfbearn as th'eypass through ysaidaperture, afp'air (5f-electrodes positioned external to the structure and aligned with the beam for forming therebetween a longitudinal annular-passage for the beam,

v 'electrode means interposed'between'said structure and said pair ofelect-rodes for converging the annular beam o'f 'relatively' large cross section into ana'nnular beam v"of relatively Smaller cross section, connection'means -for lmaintaining a D'.C. electric rviield between the Iopposite Vsurfaces of the annular aperture, andconnection means for"maintaiinfng a D.C. electric iield-between-said pair Jofel'ec'trodes.

2. 'Inlcombinatiom an electron source for forming an annular `beam of electrons, Va shielding structure partially enc'iosing'said source having an annular aperture for the passage therethrough of the annular vbeamof electrons and severed'for maintaining DC. isolation between the two opposite surfaces of the aperture, m'eans'for imparting 'a' rotational component to the electrons in said beam, a

' p'air lof electrodes positioned external tothe shielding structure 'andealigned with lthe beam `for forming theremaintaining a,D.-'C. electric field between Asaid opposite surfaces' of the` aperture, and connection' means for mainv taining a D.C. electric tield between said pair of electrodes.

3,-In combination, an annular cathode for forming an .annular electron beam of relatively'larg'e crosssection, v va structure shielding said cathode and having an annular apert'urevfor the passage therethrough of the annular beam -of electrons andV severed for maintaining AD,C. isolation 'between the two opposite surfaces of the aperture, means forming a radial magnetic eld across said aperture for imparting a rotational component to the electrons in said beam, a pair ofelectrodes positioned external to the' 'shielding structure and aligned with the 'beam for form-ing therebetween a longitudinal annular passage for the-eletcron beamand means between said annular cathode and-pair ofrelectrodesfor converging the electrons emitted from saidcathode -into acyltndrical beam of -relativelysmall-cross.section for travel through Vthe annular passagerbetween the electrodes.

4.- I'n. combination, anelect'ron source for forming an annular electron beam, a structure shielding said source and having an annular aperture for the passage therethrough of the annular beam of electrons and severed for maintaining D.C. isolation between the two opposite surfaces of the aperture, electrostatic means for imparting a rotational component to the electrons in said beam in their passage through the aperture, a pair of electrodes positioned external to the shielding structure and aligned with the source for forming therebetween a longitudinal annular passage for the beam, and electrode means interposed between said source and the pair of electrodes for forming the electron beam emitted from said source into a cylindrical annular beam for travel through said passage.

5, In combination, an electron source for forming an annular electron beam, Y av conducthtef- Structure, :yee'ni-A -rductive member `:tor forming v witness-id 'structureren-annui lar aperture for the travel on electronl iiow'fpast saidA structure, saidqstructure and said member ,forming the outer and inner surfaces, respectively of said aperture, `aplurality of conductive elementssextending;alternately from lsaidinner andouter surtacesand-faeross said ,apertureiin an interleaved pattern, connectionffmeans for maintaining said innerv and outer surfacesat different D. C. potentials, a pair of electrodes aligned with saidy source fortorming therebetween aV longitudinal annularpassagetor theelectron beam, and connection means for maintaining-.the electrode means Vat,diiferentDCspotentialsr 6. -In combination,- an annular cathode whosejfemissive surface is substantially avspherical rzone for forming a conical annular beamgoi. electrons, 2a shieldingstructure partially enclosing.r said- ,cathode and havingan anmllar aperture for passage therethroughfof. the annular beam of electrons and severed'y for 'maintaining D.C. risolation between* the two oppositesurfaces of the aperture,r connection means to saidtwoopposite-surfaces for applying a potential difference therebetween, means for imparting rotational components to theelectrons of said beam-in their :passage through` said aperture,fa y pair of electrodes Ypositioned external to the shielding structurezand aligned with `the beam lfor forming along the interspacevbetween Athe electrodes a longitudinal lannular `passage of crosssectional area small .relative Ato the emissive surface fof said cathode, means between fsaidcathode andfsaid pair of electrodes for converging `the hconical annular beam emitted: from the cathode intofa cylindrical..annularybeam 4for passage Athrough the vlongitudinal annular "passage, v and vconnection means for `maintainin'g a potential difference I between saidkpair of electrodes.

7. An elect/ron beam. system comprising an electron source, a structure forlmagnetically shielding said source and having an annular aperture for y't'hepassage ofV Athe electron flowtherethrough, lmeans 'forv creating transverse electric and magnetic iields 'across said aperture for fimparting a yrotational component lto 4the electrons emitted Yfrom said source,'a pair ot electrodes aligned with .the

Y electron source and said annular aperture for forulingan annular passage lforeli-:citron fiow therealong,A and-electrode means lfor formi-ng the electrons emitted from said V source into an annular beam for projection through saidpassage.

8. An electronic device which utilizes the` interaction rbetween an electron stream and anelecftromagnetc 'wave traveling along a wave transmission circuit characterized in that the means for forming and projecting the electron stream comprises an-elec'tron'source for forming an annular beam Vof electrons,l astructui'e shielding'. said source andrhaving an annular aperture lfor passage therethrough of the annular beam of electrons, said 'structure being v `severed for `providing D.C isolationlbetween opposite surfaceszcf said aperture, connection means for applying D. C. Ipotential across said oppositesur'facegvmeans `for imparting a rotational componentto the electrons .in said beam as they exit through saidaperturga pan-- otkelectrodes positioned external to theshieldinggtructureand aligned with .the bjeam tor j-forrning therebetween a long i-- g .tudinal annular passage tor the beam,and in tha/tithe wave transmission circuit 'along which theeleetremagetie wave travels comprises one of said pair ot electrodes,

9. An electronic device which utilizes the interaction between an electromagnetic Wave traveling along a wave transmission circuit and yan electron stream comprising an electron source providing an annular beam of elec, trons, a structure shielding said source and having an annular aperture for exit of said electron beam, means for imparting a rotational component to electrons in said beam as they traverse the aperture, a pair of electrodes defining along the -interspace therebetween an annular passage aligned with said electron source for projection therethrough of the electron stream, means between said source and the passage formed between said pair of electrodes for converging the beam emitted from said source into a beam of relatively smaller cross section for traversal of said passage, and coupling means in radio frequency energy exchange relationship with one of saidpair of tial difference across opposite surfaces of said aperture, a pair of electrodes disposed along the path of electron fiow for forming a passage for the electron flow, means for converging the beam originating from said source into a cylindrical annular beam of relatively smaller cross sectional area for projection through said passage, and coupling means in radio frequencyenergy exchange rel-ation-` ship with oue of said pair of electrodes.

11. In an electronic device, an annular cathode for forming an annular beam of electrons,a structure shielding said cathode and apertured for the traversal thereout` of the electron beam and including a hollow member extending axially through said cathode, means for imparting 4a rotational component to the electrons in said beam as they traverse the aperture, a pair of electrodes positioned external to the shielding structure for forming therebetween an annular passage for said electron flow, and coupling means extending through said hollow member in radio frequency energy exchange relationship with `the inner of said pair of electrodes.

12. In an electronic device, an electron source and a collector electrode defining therebetween a path of electron flow, a structure partially enclosing said cathode and apertured for the exit therefrom of the electron stream and severed for maintaining D. C., isolation between opposite surfaces of the aperture and including a hollow member extending axially through said cathode, means for imparting a rotational component to the electrons in said beam as they exit through the aperture, a pair of electrodes disposed for defining therebetween an annular passage which forms a portion of said path of electron flow, the inner of said pair of electrodes being a helical conductor, and coupling means in a radio frequency energy exchange relationship with said helical conductor by way of said hollow member.

13. In an electronic device, an annular electron source and atarget electrode defining therebetween a path of electron ow, a conductive structure for magnetically shielding said source, a hollow conductive member extending axially through said source for forming with said structure a relatively short annular aperture for passage of the electron flow, means for producing electric and magnetic fields across said annular aperture for imparting a rotational component to the electron flow, a pair of electrodes along said path of tiow for defining therebetween a relatively long annular passage for the electron flow, and coupling means in a radio frequency energy exchange relationship by way of said hollow member with one of said pair of cylindrical electrodes.

14. In an electronic device anannular cathode land a target electrode defining therebetween a path of electron flow, a conductive Structure for magnetically `shielding said source, a hollow conductive member extending through said annular cathode for forming with said structure a relatively short annular aperture for the exit of the electron flow from said structure, connection means for applying a potential difference across opposite surfaces of said annular aperture, means for applying a rotational component to the electron flow during passage through said aperture, a pair of electrodes along said path of ow defining therebetween a relatively long passage for the electron flow, and coaxial conductor coupling means including an inner conductor which is electrically connected to the inner of said pair of electrodes and an outer conductor which is` electrically connected to said hollow member for forming a wave guiding path through said hollow member.

l5. In an electron beam system, an annular cathode and a target electrode defining therebetween a path of electron ow, a conductive structure for magnetically shielding said source, a conductive member forming with said structure an annular aperture for the exit of the electron iiow from said structure, connection means for applying a D.C. potential across the inner and outer surfaces of said annular aperture, means for imparting a rotational component to said electrons as they traverse said aperture, a pair of electrodes along said path of flow defining therebetween an annular passage for the electron flow, and connection means for applying a` D.C. potential across the inner and outer electrodes forming the annular passage.

16. In an electron beam system, an annular cathode and target electrode defining therebetween a path of electron ow, a conductive structure for magnetically shielding said source, a conductive member extending axially through said source and forming with said structure an annular aperture for the exit of the electron flow from said structure, connection means for applying a D.C. potential across the inner and outer surfaces of said annular aperture, means for imparting a rotational component to the electrons as they traverse the aperture, a pair of electrodes along said path of flow defining therebetween an annular passage for the electron iiow, con nection means for applying a D.C. potential across said pair of electrodes, and electrode means for forming the electrons emitted from said cathode into an annular beam of relatively large cross section for passage through said annular passage and reforming said beam into an annular beam of relatively small cross section for travel through said annular passage.

References Cited in the file of this patent UNITED STATES PATENTS 2,064,469 Hael Dec. 15, 1936 2,579,654 Derby Dec. 25, 1951 2,591,350 Gorn Apr. 1, 1952 2,608,668 Hines Aug. 26, 1952 2,610,308 Touraton et al Sept. 9, 1952 2,645,737 Field July 14, 1953 2,687,490 Richet al Aug. 24, 1954 

